Spindle motor and bearing assembly

ABSTRACT

The fixed shaft type spindle motor of the invention has a fixed shaft vertically installed on a base and a rotor hub supported to freely rotate by the fixed shaft through a bearing. The bearing is composed of a compound ball bearing, and a larger diameter portion of a stepped top-form connection member having the larger diameter portion and a smaller diameter portion is fixedly engaged with the upper end of the outer ring of the compound ball bearing. And, the smaller diameter portion of the connection member is fastened to the rotor hub. The rotary shaft type spindle motor has a rotary shaft vertically installed on the rotor hub, in which the rotary shaft is supported to freely rotate on the base through the bearing. The bearing is composed of a compound ball bearing, and the larger diameter portion of the stepped top-form connection member having the larger diameter portion and the smaller diameter portion is fixedly engaged with the lower end of the outer ring of the compound ball bearing. And, the smaller diameter portion of the connection member is fastened to the base. The compound ball bearing, the shaft (the fixed shaft, the rotary shaft), and the connection member may be assembled in advance integrally in one unit, and the compound ball bearing may be replaced by a fluid bearing. The above configuration will enhance the reliability of the run-out accuracy/NRRO, the noises, the acoustic life, and the rigidity etc., of the spindle motor, and reduce the manufacturing cost.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a spindle motor and a bearingassembly for use in office automation equipment such as a computer andperipheral equipment thereof as a driving device/component for therotating mechanism thereof, specifically to the spindle motor and thebearing assembly that achieve to enhance the run-outaccuracy/nonrepeatable runout (NRRO) of a motor, and the reliability ofthe noises, acoustic life, and rigidity, etc.

[0003] 2. Description of the Prior Art

[0004] The spindle motor for driving a magnetic disk on a hard diskdrive as a peripheral equipment of a computer is classified broadly intotwo types in terms of the structure: the fixed shaft type in which afixed shaft is installed upright on a base, and a rotor hub is supportedto freely rotate by the fixed shaft through a bearing interposed betweenthe fixed shaft and the rotor hub ; and the rotary shaft type in which arotary shaft is vertically installed on a rotor hub, and the rotaryshaft is supported to freely rotate on a base through a bearinginterposed between the rotary shaft and the base.

[0005] Generally, the fixed shaft type is provided with, as shown inFIG. 9, a base (flange) 02, a fixed shaft 010 that is installed uprighton the base 02, a rotor hub (hub member) 03 that rotates relatively tothe base 02, and a bearing means 04 interposed between the fixed shaft010 and the rotor hub 03. A recording medium such as a magnetic disk(not shown) is mounted on the rotor hub 03. A stator 015 is installed onthe outer peripheral surface of an inner cylindrical wall 014 of thebase 02, and a permanent magnet 016 is installed on the inner peripheralsurface of an outer circumferential wall 013 of the rotor hub 03 so asto face the outer peripheral surface of the stator 015. The symbol 017denotes a feeder part to the windings of the stator 015, which isconnected to a flexible printed circuit board 037.

[0006] The bearing means 04 employs a compound ball bearing, and aninner ring 06 thereof is applied from the outside to the fixed shaft 010to be fixedly engaged with the shaft, and an outer ring 05 thereof isapplied from the inside to the inner peripheral surface of an innercircumferential wall 032 of the rotor hub 03 to be fixedly engaged withthe wall. A part of the inner ring 06 can be formed integrally with thefixed shaft 010 according to circumstances, as shown in FIG. 9; and theouter ring 05 can be formed commonly integrally throughout the wholestructure of the compound ball bearing in certain cases, as shown in thesame figure.

[0007] The rotary shaft type is also provided with, as shown in FIG. 10,the base (flange) 02, the rotor hub (hub member) 03 that rotatesrelatively to the base , a rotary shaft 020 that is vertically installedon the rotor hub 03, and the bearing means 04 interposed between therotary shaft 020 and the base 02. The recording medium such as amagnetic disk (not shown) is mounted on the rotor hub 03. The stator 015is installed on the outer peripheral surface of the inner cylindricalwall 014 of the base 02, and the permanent magnet 016 is installed onthe inner peripheral surface of the outer circumferential wall 013 ofthe rotor hub 03 so as to face the outer peripheral surface of thestator 015. The symbol 017 denotes the feeder part to the windings ofthe stator 015, which is connected to a flexible printed circuit board037.

[0008] The bearing means 04 employs a compound ball bearing, and theinner ring 06 thereof is applied from the outside to the rotary shaft020 to be fixedly engaged with the shaft, and the outer ring 05 thereofis applied from the inside to the inner peripheral surface of thecylindrical wall 014 of the base 02 to be fixedly engaged with the wall.A part of the inner ring 06 can be formed integrally with the rotaryshaft 020 according to circumstances, as shown in FIG. 10; and the outerring 05 can be formed commonly integrally throughout the whole structureof the compound ball bearing in certain cases, as shown in the samefigure.

[0009] In a certain case, the rotor hub 03 and the rotary shaft 020 eachmanufactured separately can be assembled in a unit, as shown in FIG. 10;and in another case, they can be manufactured in an integral unit fromthe beginning. In the latter case, a part of the inner ring 06 cannot beformed integrally with the rotary shaft 020.

[0010] In any type of the spindle motor 01, the rotor hub 03 thereof issupported on the base 02 to freely rotate through the compound ballbearing 04 as a rolling bearing interposed between the base 02 and therotor hub 03. And, the inner ring 06 of the compound ball bearing 04 isapplied from the outside to the fixed shaft 010 vertically installed onthe base 02 or to the rotary shaft 020 vertically installed on the rotorhub 03 to be fixedly engaged therewith. The outer ring 05 thereof isapplied from the inside to the inner peripheral surface of the innercircumferential wall 032 of the rotor hub 03 or to the inner peripheralsurface of the inner cylindrical wall 014 of the base 02 to be fixedlyengaged therewith.

[0011] Now, the recent demand in the hard disk drive shows a remarkabletendency to increase the recording capacity, to enhance the impactresistance, to lower the noises, to increase the data access speed, andso forth. In order to answer these requirements, the rolling bearing ofa spindle motor has gone through improvements of the materialcomposition, enhancements of the working precision of the inner andouter rings and rolling elements, etc.

[0012] However, when the inner and outer rings and the balls (rollingelements) are made of the steels such as the bearing steels, there occurmetal contacts between the rolling surfaces of the inner and outer ringsand the surfaces of the balls, which effects galling and wearing todeteriorate the acoustic characteristic, leading to the problem of theacoustic life (recently, the life of the spindle motor is evaluated notby the fatigue life, but by the acoustic life). Further, there occurfretting corrosions (impressions, dilapidated surfaces) on the rollingsurfaces due to shocks and vibrations during transportation, which alsodeteriorates the acoustic life and the precision of rotation.

[0013] Especially in recent years, the rotational speed of a spindlemotor is increased to higher than 7200 rpm, and the rotating sound ofthe motor becomes increased to that degree, which tends to shorten theacoustic life. Also in future, a still more increase of the recordingcapacity is estimated in view of the demand of recording video imagesand so forth. In order to answer such demands and future problemsestimated, the foregoing improvements of the material composition andenhancements of the working precision and the like will not besufficient for the countermeasure.

[0014] In recent years, the ball materials have been tested and examinedwhich exceed in the non-agglutination property and the wear resistance,and the nitride silicon ceramics has been adopted as the rolling elementmaterial. There have been discussions about the limitation of therolling bearing itself, including the ceramic ball bearing made of suchnew materials, and it has been put forward to employ the fluid bearingin order to solve these problems.

[0015]FIG. 11 illustrates a rotary shaft type spindle motor 01 with sucha fluid bearing loaded. This spindle motor 01 is provided with the base(flange) 02, the rotor hub (hub member) 03 that rotates relatively tothe base 02, a rotary shaft 020 that is vertically installed on therotor hub 03, and a fluid bearing 030 interposed between the rotaryshaft 020 and the base 02.

[0016] A sleeve 031 of the fluid bearing 030 sheathes the rotary shaft020, and is applied to the inner peripheral surface of the innercylindrical wall 014 of the base 02 to be fixedly engaged with the wall.A lubricating oil is supplied into the sliding area between the sleeve031 and the rotary shaft 020, and herringbones (←shaped grooves) 033formed on the circumferential surface of the rotary shaft 020 effect toraise the pressure of the lubricating oil, along with the rotation ofthe rotary shaft 020, which floats the rotary shaft 020 up from thesleeve 031.

[0017] Although not detailed in the drawing, similar herringbones areformed on an edge surface of a thrust ring 034 fixedly engaged with thelower part of the rotary shaft 020, and a lubricating oil is suppliedinto a gap between the edge surface and an inner surface of a counterplate 037 fixedly engaged with the lower end of the sleeve 031. And, asthe rotary shaft 020 turns, the herringbones effect to raise thepressure of the lubricating oil, which makes the counter plate 037receive the thrust that acts on the rotary shaft 020.

[0018] Therefore, the base 02 supports the rotary shaft 020 of the rotorhub 03 to freely rotate through the fluid bearing 030 interposedtherebetween. The other structure of the motor is basically identical tothe spindle motor having the compound ball bearing used therein.

[0019] On the other hand, in the fixed shaft type spindle motor with afluid bearing loaded, which is not illustrated, the sleeve 031 of thefluid bearing 030 is fit to an inner peripheral surface of a wall formedon the rotor hub 03, and a fixed shaft is installed upright on the base02. And, this fixed shaft is sheathed with the sleeve 031. Therefore,the fixed shaft supports the rotor hub 03 to freely rotate through thefluid bearing 030 interposed therebetween.

[0020] Even though either the ball bearing or the fluid bearing is used,and even though the spindle motor is the fixed shaft type or the rotaryshaft type, the installation of the bearing in the spindle motor iscarried out by any one of the methods: press fitting to the counterpart(rotating components and fixed components), adhesion by adhesives, andpress-fit adhesion using both of these.

[0021] In case of the press fitting method, the shape precision(circularity, cylindricality, surface roughness) of the inner or outerperipheral surface of the counterpart gives influence to transfer theshape from the outer peripheral surface of the outer ring and the innerperipheral surface of the inner ring of the rolling bearing to therolling surfaces of the inner and outer rings, or to deform the rollingsurfaces of the inner and outer rings. Also, the external stress causedby a press fitting propagates through the outer peripheral surface ofthe outer ring or through the inner peripheral surface of the innerring, and produces permanent deformations on the rolling surfaces of theinner and outer rings through the rolling elements to give impressionsthereon, which deteriorates the reliability of the run-outaccuracy/NRRO, the noises, and the acoustic life, etc., of the motor. Inthe fluid bearing, the clearance between the sleeve and the shaftsheathed with the sleeve varies, which varies the rigidity.

[0022] And, in case of the adhesion, the stress is produced when theadhesive is hardened, which deforms the bearing, also deteriorating thereliability of the run-out accuracy, the noises, and the acoustic lifeof the motor, and so forth. Further, in the rotary shaft type spindlemotor, the assembly of the stator 015 on the outer peripheral surface ofthe cylindrical wall 014 of the base 02 gives influence to deterioratethe accuracy of the inner diameter of the cylindrical wall 014, whichbrings about deterioration of the bearing accuracy.

[0023] Further, in case of the foregoing press fitting, adhesion, orpress-fit adhesion being adopted as the method of mounting the bearing,an adhesion groove (refer to adhesion groove 040 in FIG. 9, adhesiongroove 041 in FIG. 10) for filling adhesives and a run-off groove areneeded on the bearing mounting surface on the side of the counterpart,which increases the man-hour to that extent, leading to cost increase.

SUMMARY OF THE INVENTION

[0024] The present invention has been made in view of the foregoingcircumstances, and it is an object of the invention to provide a spindlemotor and a bearing assembly that achieve to resolve the foregoingproblems of the conventional spindle motor, to remove bad influences onthe precision of the rolling surfaces of the inner and outer ringsthrough the outer peripheral surface of the outer ring and the innerperipheral surface of the inner ring of the bearing, by the stressresulting from the shape precision (circularity, cylindricality, surfaceroughness) of the inner or outer peripheral surface of the counterpartin mounting the bearing, or the stress caused by the press fitting,adhesion, or press-fit adhesion as the method of mounting the bearing,to enhance the reliability of the run-out accuracy/NRRO, the noises, andthe acoustic life, etc., of the spindle motor, and to reduce themanufacturing cost thereof.

[0025] According to the first aspect of the invention, the spindle motorto resolve the above problems is a fixed shaft type spindle motor inwhich a fixed shaft is vertically installed on a base and a rotor hub issupported to freely rotate by the fixed shaft through a bearing, whereinthe bearing is a compound ball bearing, a larger diameter portion of astepped top-form connection member having the larger diameter portionand a smaller diameter portion is fixedly engaged with an upper end ofan outer ring of the compound ball bearing, and the smaller diameterportion of the connection member is fastened to the rotor hub.

[0026] Therefore, when the bearing is composed of the compound ballbearing, the outer ring of the compound ball bearing is to be fastenedto the rotor hub through the connection member.

[0027] As a result, the rotor hub (the component on the rotating side)being one of the two counterparts (the component on the rotating sideand the component on the fixing side) that mount the compound ballbearing can be made up without the inner peripheral surface of a wall,which has conventionally been regarded as necessary to fit the outerring of the compound ball bearing thereto. Therefore, there does notexist the stress resulting from the shape precision (circularity,cylindricality, surface roughness) of the inner peripheral surface ofthe wall, or the stress caused by the press fitting, adhesion, orpress-fit adhesion as the method of mounting the bearing; accordinglydisappear bad influences on the precision of the rolling surfaces of theinner and outer rings through the outer peripheral surface of the outerring of the bearing, thereby enhancing the reliability of the run-outaccuracy/NRRO, the noises, and the acoustic life, etc., of the spindlemotor.

[0028] Further, since the rotor hub being the one of the twocounterparts that mount the compound ball bearing can be configuredwithout the inner peripheral surface of the wall, which hasconventionally been regarded as necessary to fit the outer ring of thecompound ball bearing thereto, the adhesion groove (the groove forfilling adhesives) and the run-off groove that are formed conventionallyon the inner peripheral surface of the wall become unnecessary, therebyreducing the man-hour to lower the manufacturing cost.

[0029] According to the second aspect of the invention, there isprovided a fixed shaft type spindle motor in which a fixed shaft isvertically installed on a base and a rotor hub is supported to freelyrotate by the fixed shaft through a bearing, wherein the bearing is afluid bearing, a larger diameter portion of a stepped top-formconnection member having the larger diameter portion and a smallerdiameter portion is fixedly engaged with an upper end of a sleeve of thefluid bearing, and the smaller diameter portion of the connection memberis fastened to the rotor hub.

[0030] Therefore, when the bearing is composed of the fluid bearing, thesleeve of the fluid bearing is to be fastened to the rotor hub throughthe connection member.

[0031] As a result, the rotor hub (the component on the rotating side)being one of the two counterparts (the component on the rotating sideand the component on the fixing side) that mount the fluid bearing canbe made up without the inner peripheral surface of a wall, which hasconventionally been regarded as necessary to fit the sleeve of the fluidbearing thereto. Therefore, there does not exist the stress resultingfrom the shape precision (circularity, cylindricality, surfaceroughness) of the inner peripheral surface of the wall, or the stresscaused by the press fitting, adhesion, or press-fit adhesion as themethod of mounting the bearing; accordingly disappear bad influences onthe precision of the sliding surfaces of the sleeve and the fixed shaftand the clearance between the sliding surfaces of the two through theouter peripheral surface of the sleeve of the bearing, thereby enhancingthe reliability of the run-out accuracy/NRRO, the noises, the acousticlife, and the rigidity, etc., of the spindle motor.

[0032] Further, since the rotor hub being the one of the twocounterparts that mount the fluid bearing can be configured without theinner peripheral surface of the wall, which has conventionally beenregarded as necessary to fit the sleeve of the fluid bearing thereto,the adhesion groove and the run-off groove that are formedconventionally on the inner peripheral surface of the wall becomeunnecessary, thereby reducing the man-hour to lower the manufacturingcost.

[0033] According to the third aspect of the invention, there is provideda rotary shaft type spindle motor in which a rotary shaft is verticallyinstalled on a rotor hub and the rotary shaft is supported to freelyrotate on a base through a bearing, wherein the bearing is a compoundball bearing, a larger diameter portion of a stepped top-form connectionmember having the larger diameter portion and a smaller diameter portionis fixedly engaged with a lower end of an outer ring of the compoundball bearing, and the smaller diameter portion of the connection memberis fastened to the base.

[0034] Therefore, when the bearing is composed of the compound ballbearing, the outer ring of the compound ball bearing is to be fastenedto the base through the connection member.

[0035] As a result, the base (the component on the fixing side) beingthe other one of the two counterparts (the component on the rotatingside and the component on the fixing side) that mount the compound ballbearing can be made up without the inner peripheral surface of a wall,which has conventionally been regarded as necessary to fit the outerring of the compound ball bearing thereto. Therefore, there does notexist the stress resulting from the shape precision (circularity,cylindricality, surface roughness) of the inner peripheral surface ofthe wall, or the stress caused by the press fitting, adhesion, orpress-fit adhesion as the method of mounting the bearing; accordinglydisappear bad influences on the precision of the rolling surfaces of theinner and outer rings through the outer peripheral surface of the outerring of the bearing, thereby enhancing the reliability of the run-outaccuracy/NRRO, the noises, and the acoustic life, etc., of the spindlemotor.

[0036] Further, since the base being the other one of the twocounterparts that mount the compound ball bearing can be configuredwithout the inner peripheral surface of the wall, which hasconventionally been regarded as necessary to fit the outer ring of thecompound ball bearing thereto, the adhesion groove and the run-offgroove that are formed conventionally on the inner peripheral surface ofthe wall become unnecessary, thereby reducing the man-hour to lower themanufacturing cost.

[0037] According to the fourth aspect of the invention, there isprovided a rotary shaft type spindle motor in which a rotary shaft isvertically installed on a rotor hub, and the rotary shaft is supportedto freely rotate on a base through a bearing, wherein the bearing is afluid bearing, a larger diameter portion of a stepped top-formconnection member having the larger diameter portion and a smallerdiameter portion is fixedly engaged with a lower end of a sleeve of thefluid bearing, and the smaller diameter portion of the connection memberis fastened to the base.

[0038] Therefore, when the bearing is composed of the fluid bearing, thesleeve of the fluid bearing is to be fastened to the base through theconnection member.

[0039] As a result, the base (the component on the fixing side) beingthe other one of the two counterparts (the component on the rotatingside and the component on the fixing side) that mount the fluid bearingcan be made up without the inner peripheral surface of a wall, which hasconventionally been regarded as necessary to fit the sleeve of the fluidbearing thereto. Therefore, there does not exist the stress resultingfrom the shape precision (circularity, cylindricality, surfaceroughness) of the inner peripheral surface of the wall, or the stresscaused by the press fitting, adhesion, or press-fit adhesion as themethod of mounting the bearing; accordingly disappear bad influences onthe precision of the sliding surfaces of the sleeve and the fixed shaftand the clearance between the sliding surfaces of the two through theouter peripheral surface of the sleeve of the bearing, thereby enhancingthe reliability of the run-out accuracy/NRRO, the noises, the acousticlife, and the rigidity, etc., of the spindle motor.

[0040] Further, since the base being the other one of the twocounterparts that mount the fluid bearing can be configured without theinner peripheral surface of the wall, which has conventionally beenregarded as necessary to fit the sleeve of the fluid bearing thereto,the adhesion groove and the run-off groove that are formedconventionally on the inner peripheral surface of the wall becomeunnecessary, thereby reducing the man-hour to lower the manufacturingcost.

[0041] Further, according to the fifth aspect of the invention, thebearing assembly to resolve the foregoing problems is a bearing assemblyin which an inner ring of a compound ball bearing with a pressurizationapplied is fixedly engaged with a shaft, and a larger diameter portionof a stepped top-form connection member having the larger diameterportion and a smaller diameter portion is fixedly engaged with any ofends of an outer ring of the compound ball bearing.

[0042] Therefore, since the bearing assembly according to the fifthaspect of the invention is made up as above, the compound ball bearing,the shaft, and the connection member are assembled in advance into oneassembly unit. As a result, fastening the shaft to the one of the twocounterparts (the component on the rotating side and the component onthe fixing side) that mount the bearing assembly and fastening thesmaller diameter portion of the connection member to the other one willachieve to assemble the compound ball bearing between the twocounterparts, and thus the mounting work of the compound ball bearingbecomes extremely easy to perform.

[0043] And, according to the sixth aspect of the invention, there isprovided a bearing assembly in which a sleeve of a fluid bearingsheathes a shaft, and a larger diameter portion of a stepped top-formconnection member having the larger diameter portion and a smallerdiameter portion is fixedly engaged with any of ends of the sleeve.

[0044] Therefore, since the bearing assembly according to the sixthaspect of the invention is made up as above, the sleeve of the fluidbearing, the shaft, and the connection member are assembled in advanceinto one assembly unit. As a result, fastening the shaft to the one ofthe two counterparts (the component on the rotating side and thecomponent on the fixing side) that mount the bearing assembly andfastening the smaller diameter portion of the connection member to theother one will achieve to assemble the fluid bearing between the twocounterparts, and thus the mounting work of the fluid bearing becomesextremely easy to perform.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Preferred embodiments of the present invention will be describedin detail based on the followings, wherein:

[0046]FIG. 1 is a sectional view of a fixed shaft type spindle motor inthe first embodiment of the invention;

[0047]FIG. 2 is an exploded view of the same;

[0048]FIG. 3 is a sectional view of a rotary shaft type spindle motor inthe second embodiment of the invention;

[0049]FIG. 4 is an exploded view of the same;

[0050]FIG. 5 is a sectional view of a fixed shaft type spindle motor inthe third embodiment of the invention;

[0051]FIG. 6 is an exploded view of the same;

[0052]FIG. 7 is a sectional view of a rotary shaft type spindle motor inthe fourth embodiment of the invention;

[0053]FIG. 8 is an exploded view of the same;

[0054]FIG. 9 is a sectional view of a conventional fixed shaft typespindle motor using the compound ball bearing;

[0055]FIG. 10 is a sectional view of a conventional rotary shaft typespindle motor using the compound ball bearing; and

[0056]FIG. 11 is a sectional view of a conventional rotary shaft typespindle motor using the fluid bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] The first embodiment of the invention will be described withreference to FIG. 1 and FIG. 2. FIG. 1 is a sectional view of a fixedshaft type spindle motor of the first embodiment, and FIG. 2 is anexploded view of the same.

[0058] As shown in FIG. 1 and FIG. 2, a fixed shaft type spindle motor 1relating to the first embodiment has a fixed shaft 10 installed upright(vertically upward) on a flange base 2, in which the fixed shaft 10 isfixedly engaged with a central circular hole 11 on the flange base 2. Aninner ring 6 of an upper half unit ball bearing portion of a compoundball bearing 4 is applied from the outside to the upper reduced diameterportion of the fixed shaft 10 in FIG. 1 to be fixedly engaged therewith.The inner ring 6 (the portion illustrated by (6) in the drawing) of alower half unit ball bearing portion of the compound ball bearing 4 isformed integrally with the fixed shaft 10. Here, the “unit ball bearingportion of the compound ball bearing” signifies a ball bearing portionby each stage, when plural balls (rolling elements) contained betweenthe inner and outer rings with plural stages in the axial direction arevirtually partitioned into each stage.

[0059] An outer ring 5 of the compound ball bearing 4 is formed commonlyintegrally throughout the whole structure of the compound ball bearing4. On the upper end of the outer ring 5 is formed a step portion made byenlarging the inner diameter thereof. A larger diameter portion 8 a of astepped top-form connection member 8 (without a rotary shaft) having thelarger diameter portion 8 a and a smaller diameter portion 8 b isfixedly engaged with the step portion formed on the upper end of theouter ring 5 with the larger diameter portion 8 a applied from theinside to the step portion. The smaller diameter portion 8 b of theconnection member 8 is fixedly engaged with a central circular hole 9 ofa rotor hub 3 with the smaller diameter portion 8 b applied from theinside to the central circular hole 9.

[0060] Therefore, since the rotor hub 3, connection member 8, and theouter ring 5 of the compound ball bearing 4 are coupled in one unit, therotor hub 3 is supported to freely rotate by the fixed shaft 10 of thebase 2 through the connection member 8 and the compound ball bearing 4.And, since the outer ring 5 of the compound ball bearing 4 is fixed tothe rotor hub 3 through the connection member 8, an inner peripheralsurface of a wall (refer to the inner peripheral surface of the innercircumferential wall 032 of the rotor hub 03 in FIG. 9), which hasconventionally been regarded as necessary to fit the outer ring 5 of thecompound ball bearing 4 to the rotor hub 3, becomes unnecessary, so thatthe rotor hub 3 is not provided with such inner peripheral surface.

[0061] A magnetic disk (not shown) is mounted on a mounting plane 12 ofthe rotor hub 3. The other rotating bodies requiring a high run-outaccuracy/NRRO and/or low noises can be mounted thereon.

[0062] Plural balls (rolling elements) 7 are accommodated in apressurized state between the outer ring 5 and the inner ring 6, whichare arrayed in the circumferential direction with a vertical two-stageconfiguration. The balls 7 travel on concave rolling surfaces that areformed to face each other on the inner peripheral surface of the outerring 5 and on the outer peripheral surface of the inner ring 6, whilerolling relatively to the outer ring 5 and the inner ring 6.

[0063] A stator 15 is fit onto the outer peripheral surface of an innercylindrical wall 14 of the base 2, and a permanent magnet 16 is mountedcircumferentially on the inner peripheral surface of an outercircumferential wall 13 of a larger diameter portion of the rotor hub 3so as to face the outer peripheral surface of the stator 15. The symbol17 denotes a feeder part to the windings of the stator 15, which isconnected to a flexible printed circuit board 37. The symbol 18 denotesa plaque.

[0064] In the first embodiment, the fixed shaft 10, the compound ballbearing 4, and the connection member 8 are integrally assembled inadvance as a product, as shown in FIG. 2. With the bearing assembly thusproduced, the projected end of the fixed shaft 10 thereof is fixedlyengaged with the central circular hole 11 of the base 2, and the smallerdiameter portion 8 b of the connection member 8 is fixedly engaged withthe central circular hole 9 of the rotor hub 3, whereby the fixed shafttype spindle motor 1 of the first embodiment is made up.

[0065] As the first embodiment is configured as above, when the power issupplied from the feeder part 17 connected to the flexible printedcircuit board 37 to the windings of the stator 15, according to theprinciple of the synchronous motor, the rotor hub 3 with the permanentmagnet 16 starts to rotate as one body with the connection member 8 andthe outer ring 5. That is, the rotor hub 3 is borne by the compound ballbearing 4 through the connection member 8 to rotate about the fixedshaft 10.

[0066] The first embodiment thus configured exhibits the followingeffects.

[0067] In the fixed shaft type spindle motor 1 in which the fixed shaft10 is vertically installed on the base 2 and the rotor hub 3 issupported to freely rotate by the fixed shaft 10 through the compoundball bearing 4, the outer ring 5 of the compound ball bearing 4 is fixedto the rotor hub 3 through the connection member 8; and therefore, therotor hub 3 being one of the two counterparts (the rotor hub 3 being thecomponent on the rotating side and the base 2 as the component on thefixing side) that mount the compound ball bearing 4 can be made upwithout the inner peripheral surface of a wall, which has conventionallybeen regarded as necessary to fit the outer ring 5 of the-compound ballbearing 4 to the rotor hub 3. As a result, the stress resulting from theshape precision (circularity, cylindricality, surface roughness) of theinner peripheral surface of the wall, or the stress caused by the pressfitting, adhesion, or press-fit adhesion as the method of mounting thebearing does not exist; accordingly disappear bad influences on theprecision of the rolling surfaces of the inner and outer rings 6, 5through the outer peripheral surface of the outer ring 5 of the compoundball bearing 4, so that the reliability of the run-out accuracy/NRRO,the noises, and the acoustic life, etc., of the spindle motor 1 can beenhanced.

[0068] Further, the rotor hub 3 being one of the two counterparts thatmount the compound ball bearing 4 can be configured without the innerperipheral surface of the wall, which has conventionally been regardedas necessary to fit the outer ring 5 of the compound ball bearing 4 tothe rotor hub 3; and therefore, the adhesion groove for fillingadhesives and the run-off groove that are formed conventionally on theinner peripheral surface of the wall become unnecessary, which reducesthe man-hour to lower the manufacturing cost.

[0069] Further, since the compound ball bearing 4, the fixed shaft 10,and the connection member 8 are assembled in advance into one assemblyunit, fastening the fixed shaft 10 to the base 2 being the other one ofthe two counterparts that mount the bearing assembly and fastening thesmaller diameter portion 8 b of the connection member 8 to the rotor hub3 being the one will achieve to assemble the compound ball bearing 4between these two counterparts, thus the mounting work of the compoundball bearing 4 becomes extremely easy to perform.

[0070] Since the inner ring portion (6) belonging to the lower half unitball bearing portion of the two unit ball bearing portions constitutingthe compound ball bearing 4 is formed integrally with the fixed shaft10, assembling the compound ball bearing 4, the fixed shaft 10, and theconnection member 8 in advance into one assembly unit as described abovewill produce a still greater merit, with regard to the inner ring 6 ofthe compound ball bearing 4. Assuming that these components are notassembled in advance, to mount the compound ball bearing 4 to the fixedshaft 10 with the inner ring portion (6) integrally formed will lead toa troublesome work that inserts the balls (rolling elements) 7 betweenthe outer ring 5 and the fixed shaft 10. Consequently, the mounting workof the compound ball bearing 4 will become still more complicated anddifficult.

[0071] Next, the second embodiment of the invention will be describedwith reference to FIG. 3 and FIG. 4. FIG. 3 is a sectional view of arotary shaft type spindle motor of the second embodiment, and FIG. 4 isan exploded view of the same. The parts corresponding to those of thefixed shaft type spindle motor in the first embodiment are given thesame symbols.

[0072] As shown in FIG. 3 and FIG. 4, a rotary shaft type spindle motor1 relating to the second embodiment has a rotary shaft 20 installedvertically downward on the rotor hub 3, in which the rotary shaft 20 isfixedly engaged with the central circular hole 9 on the rotor hub 3. Theinner ring 6 of the lower half unit ball bearing portion of the compoundball bearing 4 is applied from the outside to the lower reduced diameterportion of the rotary shaft 20 in FIG. 3 to be fixedly engagedtherewith. The inner ring 6 (the portion illustrated by (6) in thedrawing) of the upper half unit ball bearing portion of the compoundball bearing 4 is formed integrally with the rotary shaft 20.

[0073] The outer ring 5 of the compound ball bearing 4 is formedcommonly integrally throughout the whole structure of the compound ballbearing 4. On the lower end of the outer ring 5 is formed a step portionmade by enlarging the inner diameter thereof. The larger diameterportion 8 a of the stepped top-form connection member 8 (without arotary shaft) having the larger diameter portion 8 a and the smallerdiameter portion 8 b is fixedly engaged with the step portion formed onthe lower end of the outer ring 5 with the larger diameter portion 8 aapplied from the inside to the step portion. The smaller diameterportion 8 b of the connection member 8 is fixedly engaged with thecentral circular hole 11 of the flange base 2 with the smaller diameterportion 8 b applied from the inside to the central circular hole 11.Further, the larger diameter portion 8 a is seated on an inner surfacesurrounding the central circular hole 11 of the base 2, however it isnot necessarily seated in this manner.

[0074] Therefore, since the base 2, connection member 8, and the outerring 5 of the compound ball bearing 4 are coupled in one unit, the base2 supports the rotary shaft 20 of the rotor hub 3 to freely rotatethrough the connection member 8 and the compound ball bearing 4. And,since the outer ring 5 of the compound ball bearing 4 is fixed to thebase 2 through the connection member 8, the inner peripheral surface ofa wall (refer to the inner peripheral surface of the inner cylindricalwall 014 of the base 02 in FIG. 10), which has conventionally beenregarded as necessary to fit the outer ring 5 of the compound ballbearing 4 to the base 2, becomes unnecessary, so that the base 2 is notprovided with such inner peripheral surface. The base 2 has the innercylindrical wall 14 formed upright thereon, and the inner cylindricalwall 14 has an inner peripheral surface facing to the outer peripheralsurface of the outer ring 5. However, the outer ring 5 is not fixedlyengaged with this inner peripheral surface of the inner cylindrical wall14.

[0075] In the second embodiment, the rotary shaft 20, the compound ballbearing 4, and the connection member 8 are integrally assembled inadvance as a product, as shown in FIG. 4. With the bearing assembly thusproduced, the projected end of the rotary shaft 20 thereof is fixedlyengaged with the central circular hole 9 of the rotor hub 3, and thesmaller diameter portion 8 b of the connection member 8 is fixedlyengaged with the central circular hole 11 of the base 2, whereby therotary shaft type spindle motor 1 of the second embodiment is made up.

[0076] The second embodiment is different from the first embodiment interms of the foregoing points, however it is not different in the otherpoints of the internal structure of the compound ball bearing 4, thestructure of the motor, and so forth; and the detailed description willbe omitted.

[0077] As the second embodiment is configured as above, when the poweris supplied from the feeder part 17 connected to the flexible printedcircuit board 37 to the windings of the stator 15, the rotor hub 3 withthe permanent magnet 16 starts to rotate as one body with the rotaryshaft 20 and the inner ring 6. The base 2 supports the rotary shaft 20of the rotor hub 3 to freely rotate through the connection member 8 andthe compound ball bearing 4.

[0078] The second embodiment thus configured exhibits the followingeffects.

[0079] In the rotary shaft type spindle motor 1 in which the rotaryshaft 20 is vertically installed on the rotor hub 3 and is supported tofreely rotate through the compound ball bearing 4 on the base 2, theouter ring 5 of the compound ball bearing 4 is fixed to the base 2through the connection member 8; and therefore, the base 2 being theother one of the two counterparts (the rotor hub 3 being the componenton the rotating side and the base 2 as the component on the fixing side)that mount the compound ball bearing 4 can be made up without the innerperipheral surface of a wall, which has conventionally been regarded asnecessary to fit the outer ring 5 of the compound ball bearing 4 to thebase 2. As a result, the stress resulting from the shape precision(circularity, cylindricality, surface roughness) of the inner peripheralsurface of the wall, or the stress caused by the press fitting,adhesion, or press-fit adhesion as the method of mounting the bearingdoes not exist; accordingly disappear bad influences on the precision ofthe rolling surfaces of the inner and outer rings 6, 5 through the outerperipheral surface of the outer ring 5 of the compound ball bearing 4,so that the reliability of the run-out accuracy/NRRO, the noises, andthe acoustic life, etc., of the spindle motor 1 can be enhanced.

[0080] Further, the base 2 being the other one of the two counterpartsthat mount the compound ball bearing 4 can be configured without theinner peripheral surface of the wall, which has conventionally beenregarded as necessary to fit the outer ring 5 of the compound ballbearing 4 to the base 2; and therefore, the adhesion groove and therun-off groove that are formed conventionally on the inner peripheralsurface of the wall become unnecessary, which reduces the man-hour tolower the manufacturing cost.

[0081] Further, since the compound ball bearing 4, the rotary shaft 20,and the connection member 8 are assembled in advance into one assemblyunit, fastening the rotary shaft 20 to the rotor hub 3 being the one ofthe two counterparts that mount the bearing assembly and fastening thesmaller diameter portion 8 b of the connection member 8 to the base 2being the other one will achieve to assemble the compound ball bearing 4between these two counterparts, thus the mounting work of the compoundball bearing 4 becomes extremely easy to perform. In the other aspects,the second embodiment also exhibits the same effects as those by thebearing assembly in the first embodiment.

[0082] Next, the third embodiment of the invention will be describedwith reference to FIG. 5 and FIG. 6. FIG. 5 is a sectional view of thefixed shaft type spindle motor of the third embodiment, and FIG. 6 is anexploded view of the same. The parts corresponding to those of the fixedshaft type spindle motor in the first embodiment are given the samesymbols.

[0083] As shown in FIG. 5 and FIG. 6, the fixed shaft type spindle motor1 relating to the third embodiment has the fixed shaft 10 installedupright (vertically upward) on the flange base 2, in which the fixedshaft 10 is fixedly engaged with the central circular hole 11 on theflange base 2. Also, the fixed shaft 10 is sheathed with a sleeve 31 ofa fluid bearing 30.

[0084] The sleeve 31 of the fluid bearing 30 is made of a cylindricalmember of a slightly thick wall, and has the step portion formed on theupper end thereof, which is made by enlarging comparably greatly theinner diameter thereof. The larger diameter portion 8 a of the steppedtop-form connection member 8 (without a rotary shaft) having the largerdiameter portion 8 a and the smaller diameter portion 8 b is fixedlyengaged with the step portion formed on the upper end of the sleeve 31with the larger diameter portion 8 a applied from the inside to the stepportion. The smaller diameter portion 8 b of the connection member 8 isfixedly engaged with the central circular hole 9 of the rotor hub 3 withthe smaller diameter portion 8 b applied from the inside to the centralcircular hole 9.

[0085] Therefore, since the rotor hub 3, connection member 8, and thesleeve 31 of the fluid bearing 30 are coupled in one unit, the rotor hub3 is supported to freely rotate by the fixed shaft 10 of the base 2through the connection member 8 and the fluid bearing 30. And, since thesleeve 31 of the fluid bearing 30 is fixed to the rotor hub 3 throughthe connection member 8, the inner peripheral surface of a wall, whichhas conventionally been regarded as necessary to fit the sleeve 31 ofthe fluid bearing 30 to the rotor hub 3, becomes unnecessary, so thatthe rotor hub 3 is not provided with such inner peripheral surface. Therotor hub 3 has an inner peripheral surface facing to the outerperipheral surface of the sleeve 31 of the fluid bearing 30 on thecircumferential wall 32 of the central smaller diameter portion thereof.However, the sleeve 31 is not fixedly engaged with this inner peripheralsurface of the circumferential wall 32.

[0086] A magnetic disk (not shown) is mounted on the mounting plane 12of the rotor hub 3. The other rotating bodies requiring a high run-outaccuracy/NRRO and/or low noises can be mounted thereon.

[0087] A lubricating oil is filled up in the gap between the sleeve 31of the fluid bearing 30 and the fixed shaft 10 so as not to leak out.The fixed shaft 10 has herringbone grooves 33 formed on the outercircumferential surface thereof at two places separated in the axialdirection. As described later, as the rotor hub 3 rotates, the pressureof the lubricating oil in the herringbone grooves 33 rises, whereby thesleeve 31 is floated up from the fixed shaft 10. Here, a gaseouslubricant may replace the lubricating oil.

[0088] A cylindrical thrust ring 34 is fixedly engaged with an upper endof the fixed shaft 10 by the press fitting. The thrust ring 34 isaccommodated in a concave space surrounded by the inner surface of theconnection member 8 and a step portion 36 that is formed by enlargingcomparably small the inner diameter of the upper end of the sleeve 31.When the sleeve 31 rotates integrally with the rotor hub 3, the thrustring 34 rotates in the concave space relatively to the sleeve 31.

[0089] Although not detailed in the drawing, herringbones similar to theherringbones 33 formed on the outer circumferential surface of the fixedshaft 10 are formed on an edge surface of the thrust ring 34. And, sincethe lubricating oil is supplied into a gap between the edge surface andthe inner surface of the connection member 8 that faces to the edgesurface, as the thrust ring 34 rotates relatively to the sleeve 31, theherringbones effect to raise the pressure of the lubricating oil, whichfloats the connection member 8 up from the edge surfaces of the thrustring 34 and the fixed shaft 10. In this manner, the thrust force actingon the connection member 8 is received by the fixed shaft 10, finally bythe base 2.

[0090] And, although not detailed in the drawing, herringbones areformed on the lower edge surface of the sleeve 31. And, since thelubricating oil is supplied into a gap between the lower edge surface ofthe sleeve 31 and the inner surface near the central circular hole 11 ofthe base 2, as the sleeve 31 rotates integrally with the rotor hub 3,the herringbones formed on the lower edge surface of the sleeve 31effect to raise the pressure of the lubricating oil, which floats thesleeve 31 up from the base 2. In this manner, the base 2 also receivesthe thrust force acting on the sleeve 31.

[0091] Further, these thrust bearing structures may be used at the sametime, or one of these may be omitted.

[0092] Although not detailed in the drawing, the lubricating oils thateach lubricate a radial bearing portion (the sliding portion between thefixed shaft 10 and the sleeve 31) of the fluid bearing 30 and thrustbearing portions (the contacting/sliding portion between the thrust ring34 and the connection member 8, and the contacting/sliding portionbetween the sleeve 31 and the base 2) communicate mutually, and there isformed a closed circulating passage that circulates the lubricating oilsin a single direction with the rotation of the sleeve 31.

[0093] The stator 15 is mounted on the outer peripheral surface of theinner cylindrical wall 14 of the base 2, and the permanent magnet 16 ismounted on the inner peripheral surface of the outer circumferentialwall 13 of the rotor hub 3 so as to face the outer peripheral surface ofthe stator 15. The symbol 17 denotes a feeder part to the windings ofthe stator 15, which is connected to the flexible printed circuit board37.

[0094] In the third embodiment, the fixed shaft 10, the fluid bearing30, the connection member 8, and the thrust ring 34 are integrallyassembled in advance as a product, as shown in FIG. 6. With the bearingassembly thus produced, the projected end of the fixed shaft 10 thereofis fixedly engaged with the central circular hole 11 of the base 2, andthe smaller diameter portion 8 b of the connection member 8 is fixedlyengaged with the central circular hole 9 of the rotor hub 3, whereby thefixed shaft type spindle motor 1 of the third embodiment is made up.

[0095] As the third embodiment is configured as above, when the power issupplied from the feeder part 17 connected to the flexible printedcircuit board 37 to the windings of the stator 15, the rotor hub 3 withthe permanent magnet 16 starts to rotate as one body with the connectionmember 8 and the sleeve 31. That is, the rotor hub 3 is borne by thefluid bearing 30 through the connection member 8 to rotate about thefixed shaft 10.

[0096] The third embodiment thus configured exhibits the followingeffects.

[0097] In the fixed shaft type spindle motor 1 in which the fixed shaft10 is vertically installed on the base 2 and the rotor hub 3 issupported to freely rotate by the fixed shaft 10 through the fluidbearing 30, the sleeve 31 of the fluid bearing 30 is fixed to the rotorhub 3 through the connection member 8; and therefore, the rotor hub 3being the one of the two counterparts (the rotor hub 3 being thecomponent on the rotating side and the base 2 as the component on thefixing side) that mount the fluid bearing 30 can be made up without theinner peripheral surface of a wall, which has conventionally beenregarded as necessary to fit the sleeve 31 of the fluid bearing 30 tothe rotor hub 3. As a result, there does not exist the stress resultingfrom the shape precision (circularity, cylindricality, surfaceroughness) of the inner peripheral surface of the wall, or the stresscaused by the press fitting, adhesion, or press-fit adhesion as themethod of mounting the bearing; accordingly disappear bad influences onthe precision of the sliding surfaces of the sleeve 31 and the fixedshaft 10 and the clearance between the sliding surfaces of the two to beensured at a constant quantity through the outer peripheral surface ofthe sleeve 31 of the fluid bearing 30, so that the reliability of therun-out accuracy/NRRO, the noises, the acoustic life, and the rigidity,etc., of the spindle motor 1 can be enhanced.

[0098] Further, the rotor hub 3 being the one of the two counterpartsthat mount the fluid bearing 30 can be configured without the innerperipheral surface of the wall, which has conventionally been regardedas necessary to fit the sleeve 31 of the fluid bearing 30 to the rotorhub 3; and therefore, the adhesion groove and the run-off groove thatare formed conventionally on the inner peripheral surface of the wallbecome unnecessary, which reduces the man-hour to lower themanufacturing cost.

[0099] Further, since the fluid bearing 30, the fixed shaft 10, theconnection member 8, and the thrust ring 34 are assembled in advanceinto one assembly unit, fastening the fixed shaft 10 to the base 2 beingthe other one of the two counterparts that mount the bearing assemblyand fastening the smaller diameter portion 8 b of the connection member8 to the rotor hub 3 being the one will achieve to assemble the fluidbearing 30 between these two counterparts, thus the mounting work of thefluid bearing 30 becomes extremely easy to perform. Here, thelubricating oil is to be filled up after finishing the mounting work.

[0100] Next, the fourth embodiment of the invention will be describedwith reference to FIG. 7 and FIG. 8. FIG. 7 is a sectional view of arotary shaft type spindle motor of the fourth embodiment, and FIG. 8 isan exploded view of the same. The parts corresponding to those of therotary shaft type spindle motor in the second embodiment and those ofthe fixed shaft type spindle motor in the third embodiment are given thesame symbols.

[0101] As shown in FIG. 7 and FIG. 8, the rotary shaft type spindlemotor 1 relating to the fourth embodiment has the rotary shaft 20installed vertically downward on the rotor hub 3, in which the rotaryshaft 20 is fixedly engaged with the central circular hole 9 on therotor hub 3. Also, the rotary shaft 20 is sheathed with the sleeve 31 ofthe fluid bearing 30.

[0102] The sleeve 31 of the fluid bearing 30 is made of a cylindricalmember of a slightly thick wall, and has the step portion formed on thelower end thereof, which is made by enlarging the inner diameter thereofcomparably greatly. The larger diameter portion 8 a of the steppedtop-form connection member 8 (without a rotary shaft) having the largerdiameter portion 8 a and the smaller diameter portion 8 b is fixedlyengaged with the step portion formed on the lower end of the sleeve 31with the larger diameter portion 8 a applied from the inside to the stepportion. The smaller diameter portion 8 b of the connection member 8 isfixedly engaged with the central circular hole 11 of the base 2 with thesmaller diameter portion 8 b applied from the inside to the centralcircular hole 11.

[0103] Therefore, since the base 2, connection member 8, and the sleeve31 of the fluid bearing 30 are coupled in one unit, the base 2 supportsthe rotary shaft 20 of the rotor hub 3 to freely rotate through theconnection member 8 and the sleeve 31 of the fluid bearing 30. And,since the sleeve 31 of the fluid bearing 30 is fixed to the base 2through the connection member 8, the inner peripheral surface of a wall(refer to the inner peripheral surface of the inner cylindrical wall 014of the base 02 in FIG. 11), which has conventionally been regarded asnecessary to fit the sleeve 31 of the fluid bearing 30 to the base 2,becomes unnecessary, so that the base 2 is not provided with such innerperipheral surface. The base 2 has the inner cylindrical wall 14 formedupright thereon, and the cylindrical wall 14 has an inner peripheralsurface facing to the outer peripheral surface of the sleeve 31.However, the sleeve 31 is not fixedly engaged with this inner peripheralsurface of the cylindrical wall 14.

[0104] The cylindrical thrust ring 34 is fixedly engaged with a lowerend of the rotary shaft 20 by the press fitting. The thrust ring 34 isaccommodated in a concave space surrounded by the inner surface of theconnection member 8 and the step portion 36 that is formed by enlargingcomparably small the inner diameter of the lower end of the sleeve 31.When the rotary shaft 20 rotates, the thrust ring 34 rotates in theconcave space integrally with the rotary shaft 20.

[0105] Although not detailed in the drawing, herringbones similar to theherringbones 33 formed on the outer circumferential surface of therotary shaft 20 are formed on the edge surface of the thrust ring 34.And, since the lubricating oil is supplied into a gap between the edgesurface and the inner surface of the connection member 8 that faces tothe edge surface, as the thrust ring 34 rotates integrally with therotary shaft 20, the herringbones effect to raise the pressure of thelubricating oil, which floats the rotary shaft 20 and the thrust ring 34up from the inner surface of the connection member 8. In this manner,the thrust force acting on the rotary shaft 20 is received.

[0106] Although not detailed in the drawing, the lubricating oils thateach lubricate the radial bearing portion (the sliding portion betweenthe rotary shaft 20 and the sleeve 31) of the fluid bearing 30 and thethrust bearing portion (the contacting/sliding portion between thethrust ring 34 and the connection member 8) communicate mutually, andthere is formed a closed circulating passage that circulates thelubricating oils in a single direction with the rotation of the rotaryshaft 20. A through hole 35 shows a part of the passage.

[0107] In the fourth embodiment, the rotary shaft 20, the fluid bearing30, the connection member 8, and the thrust ring 34 are integrallyassembled in advance as a product, as shown in FIG. 8. With the bearingassembly thus produced, the projected end of the rotary shaft 20 thereofis fixedly engaged with the central circular hole 9 of the rotor hub 3,and the smaller diameter portion 8 b of the connection member 8 isfixedly engaged with the central circular hole 11 of the base 2, wherebythe rotary shaft type spindle motor 1 of the fourth embodiment is madeup.

[0108] The fourth embodiment is different from the third embodiment interms of the foregoing points, however it is not different in the otherpoints; and the detailed description will be omitted.

[0109] As the fourth embodiment is configured as above, when the poweris supplied from the feeder part 17 to the windings of the stator 15,the rotor hub 3 with the permanent magnet 16 starts to rotate as onebody with the rotary shaft 20. The base 2 supports the rotary shaft 20of the rotor hub 3 to freely rotate through the connection member 8 andthe fluid bearing 30.

[0110] The fourth embodiment thus configured exhibits the followingeffects.

[0111] In the rotary shaft type spindle motor 1 in which the rotaryshaft 20 is vertically installed on the rotor hub 3 and is supported tofreely rotate through the fluid bearing 30 on the base 2, the sleeve 31of the fluid bearing 30 is fixed to the base 2 through the connectionmember 8; and therefore, the base 2 being the other one of the twocounterparts (the rotor hub 3 being the component on the rotating sideand the base 2 as the component on the fixing side) that mount the fluidbearing 30 can be made up without the inner peripheral surface of awall, which has conventionally been regarded as necessary to fit thesleeve 31 of the fluid bearing 30 to the base 2. As a result, there doesnot exist the stress resulting from the shape precision (circularity,cylindricality, surface roughness) of the inner peripheral surface ofthe wall, or the stress caused by the press fitting, adhesion, orpress-fit adhesion as the method of mounting the bearing; accordinglydisappear bad influences on the precision of the sliding surfaces of thesleeve 31 and the rotary shaft 20 and the clearance between the slidingsurfaces of the two to be ensured at a constant quantity through theouter peripheral surface of the sleeve 31 of the fluid bearing 30, sothat the reliability of the run-out accuracy/NRRO, the noises, theacoustic life, and the rigidity, etc., of the spindle motor 1 can beenhanced.

[0112] Further, the base 2 being the other one of the two counterpartsthat mount the fluid bearing 30 can be configured without the innerperipheral surface of the wall, which has conventionally been regardedas necessary to fit the sleeve 31 of the fluid bearing 30 to the base 2;and therefore, the adhesion groove and the run-off groove that areformed conventionally on the inner peripheral surface of the wall becomeunnecessary, which reduces the man-hour to lower the manufacturing cost.

[0113] Further, since the fluid bearing 30, the rotary shaft 20, theconnection member 8, and the thrust ring 34 are assembled in advanceinto one assembly unit, fastening the rotary shaft 20 to the rotor hub 3being the one of the two counterparts that mount the bearing assemblyand fastening the smaller diameter portion 8 b of the connection member8 to the base 2 being the other one will achieve to assemble the fluidbearing 30 between these two counterparts, thus the mounting work of thefluid bearing 30 becomes extremely easy to perform. Here, thelubricating oil is to be filled up after finishing the mounting work.

[0114] In the first through fourth embodiments, it is assumed that thebearing assemblies each are applied to the spindle motors each; however,they can be applied preferably to various rotating machines that requirea high run-out accuracy/NRRO and/or low noises.

[0115] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A fixed shaft type spindle motor in which a fixedshaft is vertically installed on a base and a rotor hub is supported tofreely rotate by the fixed shaft through a bearing, wherein: saidbearing is a compound ball bearing, a larger diameter portion of astepped top-form connection member having the larger diameter portionand a smaller diameter portion is fixedly engaged with an upper end ofan outer ring of said compound ball bearing, and said smaller diameterportion of the connection member is fastened to said rotor hub.
 2. Afixed shaft type spindle motor in which a fixed shaft is verticallyinstalled on a base and a rotor hub is supported to freely rotate by thefixed shaft through a bearing, wherein: said bearing is a fluid bearing,a larger diameter portion of a stepped top-form connection member havingthe larger diameter portion and a smaller diameter portion is fixedlyengaged with an upper end of a sleeve of said fluid bearing, and saidsmaller diameter portion of the connection member is fastened to saidrotor hub.
 3. A rotary shaft type spindle motor in which a rotary shaftis vertically installed on a rotor hub and said rotary shaft issupported to freely rotate on a base through a bearing, wherein: saidbearing is a compound ball bearing, a larger diameter portion of astepped top-form connection member having the larger diameter portionand a smaller diameter portion is fixedly engaged with a lower end of anouter ring of said compound ball bearing, and said smaller diameterportion of the connection member is fastened to said base.
 4. A rotaryshaft type spindle motor in which a rotary shaft is vertically installedon a rotor hub and said rotary shaft is supported to freely rotate on abase through a bearing, wherein: said bearing is a fluid bearing, alarger diameter portion of a stepped top-form connection member havingthe larger diameter portion and a smaller diameter portion is fixedlyengaged with a lower end of a sleeve of said fluid bearing, and saidsmaller diameter portion of the connection member is fastened to saidbase.
 5. A bearing assembly in which an inner ring of a compound ballbearing with a pressurization applied is fixedly engaged with a shaft,and a larger diameter portion of a stepped top-form connection memberhaving the larger diameter portion and a smaller diameter portion isfixedly engaged with any of ends of an outer ring of said compound ballbearing.
 6. A bearing assembly in which a sleeve of a fluid bearingsheathes a shaft, and a larger diameter portion of a stepped top-formconnection member having the larger diameter portion and a smallerdiameter portion is fixedly engaged with any of ends of said sleeve.